1. Field of the Invention
This invention relates to dispersing fine particle waxes, specifically to using a high shear device to form a wax dispersion with controlled particle size.
2. Background of the Invention
Waxes, both synthetic and naturally derived, are often used in micronized or fine powder form. The particles in micronized waxes are further suspended in an organic or inorganic liquid such as water or oil. The process of micronizing wax particles is an energy intensive method that is often done in jet mills. To avoid melting of wax during milling, low temperature cryogenic gases are often employed to reduce processing temperatures thereby further increasing costs. Other techniques are also used to provide a fine-particle size wax in a liquid. Ball milling and pebble milling of waxes in a suitable solvent are often used to create a suspension of wax in solvent. These are also energy intensive techniques and require a suitable solvent (i.e. toluene, xylene) that may be undesirable for environmental and other reasons.
Micronized waxes are incorporated into scrubs to act as a mild abrasive for cleansers. European Patent EP0759971 describes the use of micronized wax in bar soap. Micronized waxes are also used in cosmetic foundation applications to provide a smooth fill for wrinkles, and for moisture resistance. For example, U.S. Patent Application No. 20040018250 describes some of the uses and benefits of waxes in cosmetic and pharmaceutical applications and highlights the undesirable effect of utilizing emulsifiers to incorporate wax in these applications. The inventor cites the use of high pressure to produce an emulsion. However, it is disclosed that the wax be incorporated into an organic carrier/solvent (e.g. silicone/glycol) prior to emulsifying. Thus, the final product is an emulsion and not a true dispersion of wax in a fluid. Micronized waxes are used in deodorants (U.S. Pat. No. 4,822,603) to aid in the pay-off and feel of a deodorant stick.
Micronized waxes are also used in ink, toner and coating and powder coating applications where they are dispersed in a vehicle to provide mar and abrasion resistance in such applications as over print varnish. Micronized waxes on the surface of a coating will also modify the slip properties of a coating to allow for stacking of documents without slipping. U.S. Pat. No. 5,643,984 describes the use of micronized wax in over print varnish.
Industrial and consumer coating applications also use micronized waxes to modify viscosity properties of paints as well as for their ability to reduce mar and abrasion. Pre dispersed micronized waxes are often made as a concentrate and then added to a coating. The micronized wax imparts a thixotropic viscosity profile to coatings that is beneficial in application of the coating as well as in reducing slump of the coating once applied.
Micronized waxes dispersed in a fluid have also recently found utility in oil drilling fluids due to their ability to reduce fluid loss in drilling mud. Additional benefits of using dispersed waxes in drilling fluids are their lubricating properties for the drill bit and their thixotropic properties. The plasticity of the waxes can also be controlled by addition of select solvents to the wax containing fluid. Modification of the plasticity of the waxes can aid is control of how the wax particles tend to agglomerate and form plugs in the porous drilling formation. US Patent Application No. 20070244013 describes the use of wax to reduce loss of drilling fluid. Control of wax particle size and wax melting temperature are important parameters of the wax dispersion. Various geological formations encountered during drilling of wells have different size pores, or holes in the drill shaft, through which drilling fluid can escape. Controlling wax particle size and plasticity can effectively plug these holes and significantly reduce fluid loss. There are may techniques cited for controlling drilling fluid loss. United States Patent No. 20070078062 describes use of an invert emulsion to form a gel that can plug the pores while drilling. These type emulsions require the use of emulsifiers that are generally undesirable in drilling fluids. Gel formation is also dependent on the ionic nature of the surrounding fluid that can vary widely in drilling fluids and can result in unstable gels. Using dispersed micronized wax avoids these issues.
Micronized wax is also used in textile lubrication to help needle and cutting processes. Micronized waxes are also used as a lubricant in metal stamping; micronized waxes are also used as mold release agents for plastic molding. Micronized wax is used as a plastic processing aid (U.S. Pat. No. 3,997,489; micronized waxes are used as ant blocking aids in various applications such as adhesives, rubber compounds and various plastics.
U.S. Pat. No. 3,432,483 describes the use of a continuous process for preparing finely divided polymers. The inventor describes a process that utilizes surfactant to produce small polyethylene spheres in the presence of water and high shear stirrer.
Unlike wax emulsions that form a continuous film when dried, wax dispersions retain discrete particle identity when dried from a carrier liquid. The particle size of a stable wax emulsion is also typically sub micron while the smallest micronized wax is generally greater than a micron in diameter. Thus, there is a need for direct conversion of wax into a dispersed form with a controlled particle size while minimizing energy consumption.